1. Field of the Invention
This invention relates in general to an MIS field effect transistor and more particular to one having a very narrow channel made by two-stage diffusion.
2. Description of the Prior Art
Double-diffused MIS transistors have been proposed in the prior art as described in Electronics issued on Feb. 15, 1971, pp 99-104. The double-diffused MIS transistor has a very narrow channel determined by a two-stage diffusion through a single mask opening. As the frequency response of any MIS transistor is determined primarily by channel length, the double-diffused MIS transistor has a good frequency response.
A substrate of a semiconductor body has usually low impurity concentration such as 10.sup.14 .about. 10.sup.16 atoms/cm.sup.3 in order that the capacitance of the P-N junction formed between the drain and the substrate is made small. Accordingly, when the substrate is grounded in order to apply ground potential to the channel region, the spreading resistance in the substrate, which is rather great, deteriorates the overall frequency response.